1. Technical Field
The present invention relates to verifying and authenticating multimedia objects, and more particularly to a system and method to combine watermarks in a plurality of multimedia components.
2. Related Art
Watermarking is the process of hiding or inserting data in multimedia objects, such as audio, video and still image content. An inserted watermark can be used for various purposes, including: (1) verification, i.e., to identify the rightful owner of the content and protect the copyrights therein; and (2) authentication, i.e., to ensure that the content has not been subjected to alteration.
In the case of watermarking for verification, the inserted watermark can be used to identify the owner of the content. Specifically, by inserting a watermark into the content, an owner can later prove ownership by extracting the watermark and showing that it matches the one originally inserted. In the case of watermarking for authentication, the inserted watermark can be used to verify the authenticity of the content by identifying content that has been tampered with. One way to achieve this is to provide a watermark that is dependent on the content. In this case, the watermark is typically a signature (or a function of the signature) of the content. This signature is chosen so that it reflects the salient characteristics of the content. Accordingly, if the content has been altered, the original watermark that reflects the original signature of the content will not match the new watermark, which reflects the signature of the tampered content.
Many different techniques for inserting watermarks in multimedia components are known. A typical watermark comprises data that can identify the owner (e.g., a visual logo) for verification; or data that captures the salient visual or auditory characteristics of the multimedia component for content authentication. In many cases, the watermark is inserted in the content without causing any perceivable change to the actual audio or video content. Thus, an end-user is generally not aware of the watermark.
A common problem, however, relates to ensuring that an inserted watermark has not been tampered with. For instance, consider the case of a watermarked video image. In a video image, successive frames tend to be almost identical due to the lack of motion between them. Such a lack of change between frames provides an opportunity for a hacker to identify or weaken the inserted watermark. For example, if a given frame is watermarked and the adjacent frame(s) are not watermarked, and are very similar to the watermarked frame, then the hacker can simply subtract the watermarked frame from the unwatermarked frame(s) to obtain the watermark. Identifying the watermark will enable the hacker to remove the watermark and even insert a different watermark to change the ownership rights. Even if the successive frames are watermarked (with different watermarks), the hacker can average the successive frames to weaken the watermark.
Accordingly, there exists a need to provide secure watermarking in multimedia objects, particularly those that include video. Without such a secure system, multimedia content will be subject to hackers who can easily defeat inserted watermarks.